JPH0990777A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly bring a photoreceptor drum into contact with an intermediate transfer belt to perform a stable transfer by specifying the distance between the rotating axial center of a transfer body and the rotating axial center of the photoreceptor drum, and the longitudinal width of the photoreceptor drum. SOLUTION: This device has photoreceptor drums 9A, 9B having images formed thereon, and an intermediate transfer belt 11 formed of a cylindrically formed rectangular belt and having a plurality of backup auxiliary rollers 57A, 57B, backup rollers 58A-58D, and transfer rollers 59A, 59B which are energized, brought into contact with the inner surface by a prescribed pressing force by shafts 53A-53H and rotatably held thereby. The images formed on the photoreceptor drums 9A, 9B are once transferred to the intermediate transfer belt 11, and then transferred to a sheet. The distance between the rotating axial center of the intermediate transfer belt 11 and the rotating axial center of the photoreceptor drum 9A, 9B is set smaller than the sum of the radius of the photoreceptor drum and the radius of the transfer belt 11, and the longitudinal width of the photoreceptor drum 9A, 9B is set smaller than the width of the intermediate transfer belt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention temporarily transfers an image formed on a photoconductor drum to a transfer body (hereinafter referred to as "intermediate transfer body") and then transfers it to a recording medium for high quality recording. The present invention relates to an image forming apparatus for obtaining an image, and particularly to improvement of an intermediate transfer member.

[0002]

2. Description of the Related Art As a method of forming a color image, a toner image of each color formed on a photoconductor is temporarily transferred to an intermediate transfer member, and after superimposing each color, the color image is transferred to a sheet to form a color image. The technique for doing so has been widely known.

As problems of such a technique, there are image distortion and color misregistration positional deviation. As a method for reducing these, Japanese Patent Laid-Open No. 265331/1993 is known.

The present technique uses an endless belt as an intermediate transfer member on which an image is transferred from a photoconductor drum on which an image is formed. Then, in order to apply a predetermined amount of load to this endless belt (hereinafter referred to as "intermediate transfer belt"), a backup roller is arranged inside the intermediate transfer belt, and the position of this backup roller is changed to make the belt. It is configured so that tension can be applied.

Therefore, when the rotation speed of the photosensitive drum fluctuates due to separation and contact of the developing device and the intermediate transfer belt, and the image distortion and the color superposition position deviation when superposing on the recording paper occur, the backup roller is used. It is possible to minimize the fluctuation of the speed of the photoconductor drum by changing the position of No. 2 by the variable means and adjusting the load of the intermediate transfer belt.

[0006]

However, in order to obtain a high-quality image, it is necessary to ensure the contact state between the photosensitive drum and the intermediate transfer belt more than the conventional technique described above.

When an image is transferred from the photosensitive drum to the intermediate transfer belt, theoretically, the two are in line contact with each other and a voltage is applied to the transfer roller, whereby the image is transferred to the intermediate transfer belt. . However, the transfer of charges and transfer of toner during transfer are transient phenomena, and a predetermined time is required for transfer. Therefore, the photoconductor drum and the intermediate transfer belt need to be close to a distance where charges can be transferred for a predetermined time or more. Therefore, the photoconductor drum and the intermediate transfer belt are brought into contact with each other on a surface having a certain width (nip width). There was a need. The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to allow a photosensitive drum and an intermediate transfer belt to come into complete contact with each other with a simple structure so that both perform transfer in a stable contact state. It is to provide an image forming apparatus capable of performing the above.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a photosensitive drum on which an image is formed, and a transfer member composed of a cylindrical belt rotatably held by bringing a plurality of rollers into contact with the inner surface thereof. In an image forming apparatus configured to transfer an image formed on a photoconductor drum to the transfer body once, and then transfer the image onto a sheet, between the center of rotation of the transfer body and the center of rotation of the photoconductor drum. Is smaller than the sum (r ₁ + r ₂ ) of the radius (r ₁ ) of the photosensitive drum and the radius (r ₂ ) of the transfer member (d <r ₁ + r ₂ ), and The width (l ₁ ) in the longitudinal direction of the body drum is smaller than the belt width (l ₂ ) of the transfer body.

According to this structure, as shown in FIG. 3, the distance (d) between the center of the rotary shaft of the intermediate transfer belt 11 and the center of the rotary shaft of the photosensitive drum 9A is the radius (r _{1 of the} photosensitive drum 9A. ) And the radius (r ₂ ) of the intermediate transfer belt 11 is smaller than the total (r ₁ + r ₂ ) (d <r ₁ + r ₂ ). Since the tracks drawn by the drum 9A overlap,
The nip width of the transfer from the photoconductor drum 9A to the intermediate transfer belt 11 is secured, and the transfer efficiency is stabilized. Moreover, since the width l ₁ in the longitudinal direction of the photoconductor drum 9A is smaller than the belt width l ₂ of the intermediate transfer belt 11, the rotation loci of the photoconductor drum 9A and the intermediate transfer belt 11 overlap to some extent (d < Even when r ₁ + r ₂ ) is applied, the belt deformation of the intermediate transfer belt 11 can be absorbed by the length of the belt, and the intermediate transfer belt 11 accurately follows the longitudinal direction of the photosensitive drum 9A and comes into contact therewith.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic view of an image forming apparatus to which the present invention is applied, and FIG. 2 is a schematic view showing an intermediate transfer belt and its peripheral mechanism.

In the image forming apparatus according to the embodiment of the present invention, as shown in FIG. 1, a light beam from a light source (not shown) is mirrored by an optical scanning system 1 including a polygon mirror 2, a lens system 3 and the like. , 6 and 7, 8 through the photosensitive drum 9
Irradiate A and 9B to form an electrostatic latent image.

On the photosensitive drum 9A, a black toner developing device 10A and a magenta color developing device 10 are provided.
B is attached, and a developing device 10C for cyan toner and a developing device 10D for yellow toner are attached to the photosensitive drum 9B.

The surfaces of the photosensitive drums 9A and 9B come into contact with the intermediate transfer belt 11 which is a rectangular belt formed in a cylindrical shape. The intermediate transfer belt 11 has a volume resistivity of 10 ¹⁰ to 1
It is a resistor in the medium resistance region of 0 ¹⁴ Ωcm and has a thickness of 15
It is about 0 μm and has almost no elasticity, and is formed of, for example, polycarbonate, polyimide, polyether or the like. Flange (described in FIG. 4 described later) is arranged at both ends of the intermediate transfer belt 11 formed in a cylindrical shape, and both ends of the intermediate transfer belt 11 are attached to the flange, and the flange is connected to a drive source to form an intermediate portion. The transfer belt 11 is configured to be rotatable.

The latent images on the photosensitive drums 9A and 9B are sequentially developed by the developing devices 10A to 10D one by one for each rotation of the drum, and are primarily transferred to the intermediate transfer belt 11 by Coulomb force. After the transfer of one color is completed, the photosensitive drums 9A and 9B are cleaned by a cleaner mechanism (not shown) to remove the residual toner, and then the other colors are transferred to the photosensitive drums 9A and 9B.
B is developed.

Specifically, black is transferred from the photosensitive drum 9A to the intermediate transfer belt 11, and then the photosensitive drum 9 is transferred.
The cyan color is transferred from the photosensitive drum 9B to the intermediate transfer belt 11 rotated to the position B.

After the black color is transferred to the intermediate transfer belt 11 of the photosensitive drum 9A, the residual toner is removed by a cleaner, the magenta color is developed, and the magenta color is transferred to the intermediate transfer belt 11.
Transfer to Similarly, on the photoconductor drum 9B, after transferring the cyan color, the residual toner is removed by a cleaner, the yellow color is developed, and the transfer is performed.

When the four color toners are transferred to the intermediate transfer belt 11, the paper stored in the paper cassette 14 passes through the reversing passages 16 and 17 by the rollers 15 and the like, and passes through the registration rollers 18 and the intermediate transfer belt. The toner that forms each image is transferred to the sheet of paper 11 and the second transfer roller 19, and the transferred sheet of paper is discharged to the carrying device 20 and is carried to the fixing unit 22 by the carrying belt 21.

In the fixing unit 22, fixing is performed by the fixing roller 23 and the pressure roller 24, and the sending roller 25 is used.
Is discharged to the outside by.

A cleaning device 13 cleans the untransferred toner on the intermediate transfer belt 11. 1
2a is a blade that directly contacts the intermediate transfer belt 11,
12b is a rubbing roller. The untransferred toner is scraped off by the blade 12a and the rubbing roller 12b, sent in the axial direction by the toner carrying device 12c, and collected in a collecting container (not shown).

Next, the intermediate transfer belt 11 and its internal structure will be described. FIG. 2 is a schematic view showing the intermediate transfer belt 11 and a mechanism around it. In the figure, the intermediate transfer belt 11 formed in a cylindrical shape surrounds the outer peripheral portion and is in contact with the photosensitive drums 9A and 9B.
However, its end is fixed to the support 36 to form a drum shape.

On the other hand, inside the intermediate transfer belt 11, a backup auxiliary roller 57A composed of a rubber roller,
57B, backup rollers 58A to 58D composed of iron rollers, first transfer rollers 59A and 59B composed of conductive rubber rollers, etc. are urged to the intermediate transfer belt 11 by a predetermined pressing force by shafts 53A to 53H. Is provided.

Shafts 53A and 53D to which backup auxiliary rollers 57A and 57B are attached, and backup roller 58
The shaft 53G to which C is attached and the shaft 53H to which the backup roller 58D is attached are the rotation center 11a of the intermediate transfer member 11.
Configured as a radial axis that radiates outward from the axis 53A
A first transfer roller 59 provided in the vicinity of and parallel to the shaft 53A.
In the vicinity of the shaft 53B with the A attached and the shaft 53D, the shaft 5
The shaft 53E having the first transfer roller 59B and the shafts 53C and 53F having the backup rollers 58A and 58B, which are provided in parallel with the 3D, extend outward from the position distant from the rotation center 11a of the intermediate transfer belt 11 to the right. Configured as an outgoing non-radial axis.

Cams 35 are provided on a support 36 at both inner ends of the intermediate transfer belt 11. When the intermediate transfer belt 11 rotates clockwise, the cam 35 separates the rollers from the intermediate transfer belt 11 and pushes down the rollers so that the rollers do not come into contact with the support 36.

Radial shafts 53A, 53D, 53G, 53H having a plurality of rollers having axial center directions radially outward from the rotation center 11a of the intermediate transfer belt 11.
And non-radial shafts 53B, 53C, 53E, 53 having an axial direction outward from a position deviated from the center of the rotation shaft.
The radial shaft and the non-radial shaft adjacent to the radial shaft are separated from each other within a range in which sliding of the rollers does not interfere with each other.

Next, the relationship between the photosensitive drum 9A and the like when using the intermediate transfer belt 11, which is a feature of the embodiment of the present invention, will be described.

FIG. 3 is a diagram showing the relationship between the photosensitive drum and the intermediate transfer drum. In the figure, the center of the rotation axis of the photosensitive drum 9A is located slightly below so that the outer periphery of the photosensitive drum 9A pushes down the intermediate transfer belt 11,
The distance (d) between the center of rotation of the intermediate transfer drum 11 and the center of rotation of the photosensitive drum 9A is the sum of the radius (r ₁ ) of the photosensitive drum 9A and the radius (r ₂ ) of the transfer belt 11 ( It is set to be smaller than (r ₁ + r ₂ ) (d <r ₁ + r ₂ ). That is, with such a configuration, the locus of rotation drawn by the intermediate transfer belt 11 and the locus drawn by the photosensitive drum 9A overlap each other, so that the nip width of the primary transfer is secured and the transfer efficiency is stabilized. This distance (d) is 0.1
0.5mm is good. If it is 0.1 or less, a sufficient nip width cannot be obtained. On the other hand, if it is 0.5 mm or more, the circular shape of the intermediate transfer belt 11 cannot be maintained, so that the transferred image such as waviness and deformation of the belt is adversely affected.

FIG. 4 is a diagram showing the relationship between the intermediate transfer belt 11 and the photosensitive drum 9A according to the present invention. A rectangular belt is formed in a circular shape and relayed by a support 36, and both ends are connected to each other. The circular flanges 11a and 11a are fixed to the support 36, and the intermediate transfer belt is attached only to the support 36.

As shown in the figure, the longitudinal width l ₁ of the photosensitive drum 9A is smaller than the belt width l ₂ of the intermediate transfer belt 11. This, even if the locus of rotation of the photosensitive drum 9A and the intermediate transfer belt 11 are overlapped to some extent _{(d <r 1 + r 2} ), a belt deformation of the intermediate transfer belt 11 width of the belt can be absorbed by a long minute The intermediate transfer belt 11 is configured so as to follow the longitudinal direction of the photosensitive drum 9A with high accuracy and come into contact with the photosensitive drum 9A.

Further, the length l ₃ between the flanges 11a of the intermediate transfer drum 11 formed in a hollow cylindrical shape by the flanges 11a on both ends is the width l _{1 of the} photosensitive drum 9A.
If it is smaller, it will come into direct line contact with the photosensitive drum,
The above-mentioned overlap cannot be achieved and a sufficient nip width cannot be obtained. However, if the width l ₁ of the photosensitive drum 9A is made smaller than at least the length l ₃ between the flanges 11a, the nip width is obtained and the transfer efficiency is improved.

[0030]

EXAMPLE The length of the photosensitive drums 9A and 9B is 110 mm,
The width of the intermediate transfer belt 11 is 280 to 350 mm. Diameter of photoconductor drum is 50mm, diameter of intermediate transfer belt is 150m
m, the distance d between the axis of the photosensitive drum and the axis of the intermediate transfer belt was set to 199.8 mm, and the respective loci were overlapped to form a color image device.

FIG. 5 is a diagram showing the relationship between the layout of the intermediate transfer belt and the image density. The image density is plotted on the vertical axis and the transfer voltage is plotted on the horizontal axis. The measured values of the layout X of the present invention and the conventional layout Y are shown. It is the figure which plotted.

Layout X in which the longitudinal width l ₁ of the photosensitive drum is smaller than the belt width l ₂ of the intermediate transfer belt
It can be understood that the margin of setting the transfer voltage is increased.

[0033]

As described above, according to the structure of the present invention, since the loci of the photosensitive drum and the intermediate transfer belt overlap each other, the photosensitive drum and the intermediate transfer belt are completely formed with a simple structure. By making contact, the nip width can be increased and transfer can be performed in a stable contact state. Further, since the width of the photosensitive drum in the longitudinal direction is shorter than the width of the intermediate transfer belt, there is a remarkable effect such that the bending in the width direction can be absorbed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus to which the present invention is applied.

FIG. 2 is a schematic view showing an intermediate transfer belt and a mechanism around the intermediate transfer belt.

FIG. 3 is a relationship diagram between a photosensitive drum and an intermediate transfer belt.

FIG. 4 is a relationship diagram of a photosensitive drum and an intermediate transfer belt.

FIG. 5 is a relationship diagram between a transfer voltage of a transfer roller and an image density.

[Explanation of symbols]

 9: Photosensitive drum 11: Intermediate transfer drum 12: Driving source 19: Second transfer roller 20: Conveying device 22: Fixing unit 11: Intermediate transfer belt 57: Backup auxiliary roller 58: Backup roller 59: First transfer roller

Claims (1)

[Claims] 1. A photoconductor drum on which an image is formed, and a transfer body composed of a cylindrical belt rotatably held by bringing a plurality of rollers into contact with an inner surface of the photoconductor drum, and the photoconductor drum formed on the photoconductor drum. In an image forming apparatus configured to transfer an image to a transfer body once and then to a sheet, a distance (d) between a rotation axis center of the transfer body and a rotation axis center of the photosensitive drum is set to The radius (r ₁ ) of the body drum and the radius (r ₂ ) of the transfer body are smaller than the total (r ₁ + r ₂ ) (d <r ₁ + r ₂ ), and the width of the photoconductor drum in the longitudinal direction ( An image forming apparatus, wherein l ₁ ) is smaller than the belt width (l ₂ ) of the transfer body.